The entry of foreign matter into an aircraft engine can cause damage to engine components resulting in engine performance degradation. Large particles of ice or gravel can cause instant measurable performance degradation. Smaller particles will cause erosion which in turn causes measurable performance degradation over longer periods of time. In a turbofan or bypass engine the most serious foreign matter damage occurs when the foreign matter enter the engine core. Major increases in fuel consumption result from foreign object damage and foreign matter caused wear to the compressor and turbine parts in the engine core. Also, the ingestion of water, snow, slush, ice, etc. into the engine core can cause engine flame out. Herein the term "foreign matter" is used to denote any objects or particles matter having the capability of causing wear or damage, or a flame out, if allowed entry into the core section of the engine, including gravel, dirt, ice, slush, snow, and water.
It is well known that unrestrained particles with tangential velocity move outward of are centrifuged away from the center of rotation. This invention involves choosing engine fan geometry on new designs or modifying by adding hardware to existing engines which will impart tangential velocity early enough to centrifuge particles outside the capture area of the engine core, or altering the existing design to increase the axial space between the fan rotor and the core inlet lip.
A particle which enters a rotating fan is accelerated in the tangential direction and hence is also accelerated in the radial direction. If the axial travel between the point where angular and radial accelerations are imparted to the particle and the lip of the core engine inlet (or splitter between the core and fan duct) is long enough, the particle will travel far enough radially to miss the core and exit through the fan duct. This invention uses these principles to design new engines or modify existing engines to dramatically reduce core FOD and resulting engine deterioration. It also will increase the potential for operating airplanes on "dirty runways" such as for military applications.